DOUBLE AND TRIPLE RESONANCE EXPERIMENTS ON 2-BROMO-5-CHLOROTOLUENE: SIGNS OF THE RING AND RING-METHYL PROTON COUPLING CONSTANTS

1966 ◽  
Vol 44 (22) ◽  
pp. 2743-2747 ◽  
Author(s):  
G. Kotowycz ◽  
T. Schaefer
Keyword(s):  
Coupling Constants ◽  
Para Position ◽  
Triple Resonance ◽  
Triple Resonance Experiments ◽  
Methyl Proton ◽  
Methyl Group ◽  
Meta Position ◽  
Proton Coupling ◽  
Polarization Mechanism ◽  
Exchange Polarization

Tickling and decoupling (triple resonance) techniques show that the ortho, meta, and para proton coupling constants have the same sign in 2-bromo-5-chlorotoluene. If the ortho coupling in the ring is positive, then decoupling experiments show that the methyl proton couplings to the ring protons in the ortho and para position to the methyl group are negative, while that to the meta position is positive. These signs are in agreement with the σ–π exchange polarization mechanism.

Concerning a relationship between long-range ring proton – methyl proton coupling constants and mobile bond order

1968 ◽  
Vol 46 (4) ◽  
pp. 654-656 ◽  
Author(s):  
D. J. Blears ◽  
S. S. Danyluk ◽  
T. Schaefer
Keyword(s):  
Linear Relationship ◽  
Long Range ◽  
Bond Order ◽  
Coupling Constants ◽  
Methyl Proton ◽  
Methyl Group ◽  
Potential Barriers ◽  
Proton Coupling ◽  
Induced Changes ◽  
Excitation Parameters

Long-range proton – methyl proton coupling constants in propene, mesitylene, 9-methylphenanthrene, and acenaphthene appear to be linearly related to the square of the mobile bond order between the carbon atoms bonded to the methyl group and the proton. However, substituent-induced changes in the charge on and hybridization state of the carbon atoms, in excitation parameters and in potential barriers to rotation of the methyl group, may also affect the coupling. Such changes must be considered in the application of a possible linear relationship.

ESR and ENDOR Investigations of Adrenochrome Semiquinone and Related Amino-1,2-Benzosemiquinone Radicals

1985 ◽  
Vol 40 (7-8) ◽  
pp. 531-534 ◽  
Author(s):  
Hartmut B. Stegmann ◽  
Hoang Dao-Ba ◽  
Klaus Scheffler ◽  
Martin G. Peter
Keyword(s):  
Hyperfine Structure ◽  
Spin Density ◽  
Ethanol Solution ◽  
Coupling Constants ◽  
Triple Resonance ◽  
Triple Resonance Experiments ◽  
Proton Coupling ◽  
Endor Spectroscopy ◽  
Nitrogen Coupling

Abstract Dimethyl or diethylamine reacts very smoothly in ethanol solution with catechols to the corresponding aminoquinones. The paramagnetic intermediates, the semiquinones, are investigated by ESR and ENDOR spectroscopy using the spin stabilisation technique with diarylthallium cations. The spectra of these radicals show clearly the thallium and nitrogen coupling and the hydrogen hyperfine structure. For some examples the signs of the proton coupling constants are determined by TRIPLE resonance experiments. The results indicate a negative spin density in one position of the unsymmetrically substituted radical 3. With the results obtained for the monocyclic aminosemiquinones the hyperfine structure of the adrenochrome semiquinone is analysed.

Strongly hindered rotation in α,α,2,6-terrachlorotoluene. Stereospecific five-bond coupling. Hyperconjugative contributions to long-range sidechain-ring proton coupling constants

1968 ◽  
Vol 46 (12) ◽  
pp. 2187-2188 ◽  
Author(s):  
T. Schaefer ◽  
R. Schwenk ◽  
C. J. Macdonald ◽  
W. F. Reynolds
Keyword(s):  
Free Energy ◽  
Resonance Spectrum ◽  
Coupling Constants ◽  
Proton Resonance ◽  
Kcal Mole ◽  
Hindered Rotation ◽  
Ring Proton ◽  
Meta Position ◽  
Proton Coupling ◽  
Free Energy Of Activation

At −40 °C the C—H bond of the dichloromethyl group of α,α,2,6-tetrachlorotoluene lies in the plane of the ring. The proton resonance spectrum demonstrates a stereospecific five-bond coupling between the C—H proton and the ring proton in the meta position. The coupling to the para proton is essentially zero as expected from a hyperconjugative mechanism. The free energy of activation of rotation of the dichloromethyl group is about 15 kcal/mole at 25 °C.

scholarly journals Signs of proton–proton and proton–fluorine spin–spin coupling constants in 2-fluoro-3-methylpyridine. Sigma and pi contributions to coupling in a nitrogen heterocycle

1969 ◽  
Vol 47 (9) ◽  
pp. 1507-1514 ◽  
Author(s):  
T. Schaefer ◽  
S. S. Danyluk ◽  
C. L. Bell
Keyword(s):  
Nitrogen Atom ◽  
Long Range ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Nitrogen Heterocycle ◽  
Triple Resonance ◽  
Triple Resonance Experiments ◽  
Proton Proton ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The signs of all proton–proton and proton–fluorine spin–spin coupling constants in 2-fluoro-3-methylpyridine have been determined by double and triple resonance experiments. The signs of the longrange coupling constants, JH,CH3 and JF,CH3 are the same as in fluorotoluene derivatives. Their magnitudes are consistent with the assumption that the nitrogen atom primarily polarizes the σ bonds in the molecule, leaving the π contribution to the long-range coupling relatively unaffected.

Impact of Transverse Relaxation Optimized Spectroscopy (TROSY) on NMR as a technique in structural biology

2000 ◽  
Vol 33 (2) ◽  
pp. 161-197 ◽  
Author(s):  
Konstantin Pervushin
Keyword(s):  
Resonance Assignment ◽  
Structure Determination ◽  
Isotope Labeling ◽  
Molecular Size ◽  
Coupling Constants ◽  
Scalar Coupling ◽  
Triple Resonance ◽  
Single Quantum ◽  
Triple Resonance Experiments ◽  
Transverse Relaxation

1. Transverse relaxation and the molecular size limit in liquid state NMR 1612. TROSY: how does it work? 1632.1 Transverse relaxation in coupled spin systems 1632.2 The TROSY effect, relaxation due to remote protons and 2H isotope labeling 1653. Direct heteronuclear chemical shift correlations 1683.1 Single-Quantum [15N,1H]-TROSY 1683.2 Zero-Quantum [15N,1H]-TROSY 1713.3 Single-Quantum TROSY with aromatic 13C–1H moieties 1764. Resonance assignment and NOE spectroscopy of large biomolecules 1804.1 TROSY-based triple resonance experiments for 13C, 15N and 1HN backbone resonance assignment in uniformly 2H, 13C, 15N labeled proteins 1804.2 TROSY-type NOE spectroscopy 1865. Scalar coupling across hydrogen bonds observed by TROSY 1876. The use of TROSY for measurements of residual dipolar coupling constants 1907. Conclusions 1918. Acknowledgements 1919. References 191The application of nuclear magnetic resonance (NMR) spectroscopy for structure determination of proteins and nucleic acids (Wüthrich, 1986) with molecular mass exceeding 30 kDa is largely constrained by two factors, fast transverse relaxation of spins of interest and complexity of NMR spectra, both of which increase with increasing molecular size (Wagner, 1993b; Clore & Gronenborn, 1997, 1998b; Kay & Gardner, 1997). The good news is that neither of these factors represent a fundamental limit for the application of NMR techniques to protein structure determination in solution (Clore & Gronenborn, 1998a; Wüthrich, 1998; Wider & Wüthrich, 1999). In fact, in the past few years the size limitations imposed by these factors have been pushed up to 50–70 kDa by the use of 13C, 15N and 2H isotope labeling combined with selective reprotonation of individual chemical groups in conjunction with the use of triple-resonance experiments (Bax, 1994; Gardner et al. 1997; Gardner & Kay, 1998) and heteronuclear-resolved NMR (Fesik & Zuiderweg, 1988; Marion et al. 1989a; Otting & Wüthrich, 1990). Among the largest biomolecules whose 3D structure was solved by NMR are the 44 kDa trimeric ectodomain of simian immunodeficiency virus (SIV) gp41 (Caffrey et al. 1998) and 40–60 kDa particles of the elongation initiation factor 4E solubilized in CHAPS micelles (Matsuo et al. 1997; McGuire et al. 1998).

scholarly journals 13C NMR of the Tetrakis(phenylethynyl)borate Anion and of Some Phenylethynyl Boranes

1982 ◽  
Vol 37 (6) ◽  
pp. 788-789 ◽  
Author(s):  
Bernd Wrackmeyer
Keyword(s):  
13C Nmr ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Triple Resonance ◽  
Triple Resonance Experiments ◽  
Nmr Parameters ◽  
C Nmr

Abstract The 13C NMR parameters of the title compounds are assigned by heteronuclear triple resonance experiments 13C{1H,11B}. The magnitude of the coupling constants J(13C11B) corresponds roughly with J(13C13C). The chemical shifts δ13C reveal B-C(pp) π bonding which is, however, rather weak when compared with C+-C(pp) π bonding in phenylethynyl carbocations.

Solvent effects on the proton spectra of some halopropenes. The preparation and proton resonance spectra of the 1-iodopropenes

1967 ◽  
Vol 45 (10) ◽  
pp. 1081-1087 ◽  
Author(s):  
F. Hruska ◽  
D. W. McBride ◽  
T. Schaefer
Keyword(s):  
Hydrogen Bonding ◽  
Solvent Effects ◽  
Olefinic Proton ◽  
Coupling Constants ◽  
Proton Resonance ◽  
Methyl Proton ◽  
Reaction Field ◽  
Field Effects ◽  
Proton Coupling ◽  
Solvent Shifts

The preparation and proton resonance spectra of the 1-iodopropenes are reported and solvent effects on the proton spectra of the chloro-, bromo-, and iodo-compounds are measured. The proton coupling constants are discussed in terms of old and new electronegativity correlations. The olefinic cis and trans proton shifts can be attributed mainly to a paramagnetic contribution from the substituent, whereas the gem olefinic proton shifts depend in addition on the electron-withdrawing power of the substituent. The methyl proton shifts in the 1-substituted compound show little dependence on the substituent and this is discussed in relation to the barrier heights to methyl rotation. The solvent shifts in benzene cannot be completely reconciled with a dipole – induced dipole model. They increase with the size of the substituent and are largest for protons farthest from the substituent. The solvent shifts in acetone can be explained as due to weak hydrogen bonding and reaction field effects. The shifts of protons gem to the substituent arise mainly from hydrogen bonding, whereas the shifts of protons cis or trans have significant contributions from both effects. The reaction field effects can also account for the methyl shifts in acetone.

Long-range Proton–Proton Coupling Constants in the Vinylpyridines. Conformational Preferences of the Vinyl Group and Molecular Orbital Calculations

1974 ◽  
Vol 52 (1) ◽  
pp. 136-142 ◽  
Author(s):  
J. Brian Rowbotham ◽  
Ted Schaefer
Keyword(s):  
Molecular Orbital ◽  
Long Range ◽  
Coupling Constants ◽  
Graphical Form ◽  
Molecular Orbital Calculations ◽  
Proton Proton ◽  
Meta Position ◽  
Proton Coupling ◽  
Conformational Preferences ◽  
Vinyl Group

The p.m.r. spectra of 2-vinylpyridine, 2-methyl-5-vinylpyridine, and 4-vinylpyridine are examined for long-range coupling constants between the vinylic and ring protons. Those over six, seven, and eight bonds from the vinyl group to ring or methyl protons in the para position are dominated by a π electron mechanism. Those over five bonds between the α proton and a ring proton in the meta position indicate that the vinyl group prefers to lie cis to the nitrogen in 2-vinylpyridine but trans in the 5-vinylpyridine. INDO-MO-FPT calculations of coupling constants between vinyl protons and ring protons, carbon-13, and nitrogen-14 nuclei are presented in graphical form.

11B- und 13C-NMR-Spektroskopie von nido-Hexaalkyl-2.3.4.5-tetracarbahexaboranen(6) / 11B- und 13C-NMR Spectroscopy of nido-Hexaalkyl-2,3,4,5-tetracarbahexaboranes(6)

1982 ◽  
Vol 37 (4) ◽  
pp. 412-419 ◽  
Author(s):  
Bernd Wrackmeyer
Keyword(s):  
Nmr Spectroscopy ◽  
13C Nmr ◽  
13C Nmr Spectroscopy ◽  
Coupling Constants ◽  
Triple Resonance ◽  
Triple Resonance Experiments ◽  
Nmr Data ◽  
Nuclear Shielding ◽  
C Nmr

11B and 13C NMR data of peralkylated nido-2,3,4,5-tetracarbahexaboranes(6) are reported. Application of selective heteronuclear triple resonance experiments 13C{1H,11B} enables to assign the structures of various isomers. The magnitude of the coupling constants 1J(11B11B), 1J(13C11B) and 1J(13C13C) is in accord with expectations based on the conception of bonding in carboranes. The comparison of δ11B and δ13C data of the nido- 2,3,4,5-tetracarboranes(6) with δ13C-data of corresponding non-classical carbocations shows the influence of charge upon the nuclear shielding of carbon in the latter.

Notizen: Determination of Signs of Coupling Constants for (Ethene)bis- (triphenylphosphane)platinum(0)

1997 ◽  
Vol 52 (8) ◽  
pp. 1019-1022 ◽  
Author(s):  
Bernd Wrackmeyer
Keyword(s):  
Coupling Constants ◽  
Triple Resonance ◽  
Two Dimensional ◽  
Triple Resonance Experiments

The signs of coupling constants [ 1J(195Pt,13C) (> 0), 2J(195Pt,1H) (< 0), ∑2J (31P,13C)trans + 2J(31P,13C)cis (> 0) and ∑3J(31P,1H )trans +3J(31P,1H)cis (< 0)] in (ethene)bis(triphenylphosphane) platinum (0) (1) were determined by selective heteronuclear double and triple resonance experiments of the type 1H{31P}, 13C{1H,31P} and two-dimensional heteronuclear shift correlations (HETCOR) of the type 13C/1H, 195Pt/1H, and 31P/1H, either by observing the heteronucleus or 1H in the more sensitive inverse mode.

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